Extrinsic Calibration of a Laser Galvanometric Setup and a Range Camera.

Seppe Sels,Rudi Penne,Steve Vanlanduit,Boris Bogaerts

doi:10.3390/s18051478

Abstract

Currently, galvanometric scanning systems (like the one used in a scanning laser Doppler vibrometer) rely on a planar calibration procedure between a two-dimensional (2D) camera and the laser galvanometric scanning system to automatically aim a laser beam at a particular point on an object. In the case of nonplanar or moving objects, this calibration is not sufficiently accurate anymore. In this work, a three-dimensional (3D) calibration procedure that uses a 3D range sensor is proposed. The 3D calibration is valid for all types of objects and retains its accuracy when objects are moved between subsequent measurement campaigns. The proposed 3D calibration uses a Non-Perspective-n-Point (NPnP) problem solution. The 3D range sensor is used to calculate the position of the object under test relative to the laser galvanometric system. With this extrinsic calibration, the laser galvanometric scanning system can automatically aim a laser beam to this object. In experiments, the mean accuracy of aiming the laser beam on an object is below 10 mm for 95% of the measurements. This achieved accuracy is mainly determined by the accuracy and resolution of the 3D range sensor. The new calibration method is significantly better than the original 2D calibration method, which in our setup achieves errors below 68 mm for 95% of the measurements.

Highlights

Introduction and Related WorkLaser galvanometric systems are systems commonly used for laser projection systems, optical measurement devices, and projection based systems
Laser galvanometers can be used in combination with camera systems to provide feedback about the laser spot position
When the laser galvanometer system and the camera system are extrinsically calibrated, the laser galvanometer can aim the laser spot to a position predefined in the camera coordinate system

Summary

Introduction

Introduction and Related WorkLaser galvanometric systems (abbreviated to laser galvanometers) are systems commonly used for laser projection systems, optical measurement devices, and projection based systems. The instrument is able to move the laser spot to different positions on the object. The angle of a mirror can be altered by a galvanometer motor. These moving mirrors are used to deflect a laser beam to a certain position. When the laser galvanometer system and the camera system are extrinsically calibrated, the laser galvanometer can aim the laser spot to a position predefined in the camera coordinate system. Extrinsic calibration calculates the position (rotation and translation) between the camera and laser galvanometer in a reference coordinate system. This calibration assumes that the intrinsic parameters of both the laser galvanometer and camera are known

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Conclusion